1. Technical Field
Embodiments of the present disclosure relate to an optical writing device that forms an electrostatic latent image on an image carrier based on image information and an image forming apparatus, such as a copier, a printer, a facsimile machine, a plotter, or a multifunction machine including at least one of these apparatuses, including the optical writing device.
2. Related Art
A polygon scanner (hereinafter also referred to as a polygon mirror) serving as an optical deflector employed in an optical writing device is a multifaceted mirror rotated at high speed by a motor that generates heat, thereby generating hot air and increasing the temperature of a nearby scanning lens or the like. Such an increase in the temperature of the scanning lens or the like is known to degrade magnification and other characteristics of scanning lines and cause color shift.
Measures addressing this issue include reducing the rotation rate of the polygon scanner to reduce the amount of heat generated by the polygon scanner and minimizing a so-called A-size of the polygon scanner; i.e., the radius of the polygon scanner to a mirror surface thereof. There is also a method of providing soundproof glass or the like to prevent transmission of the hot air from the polygon scanner to an optical element such as the scanning lens, to thereby block the hot air. However, the soundproof glass is disposed at a position at which a beam from a light source is not yet incident on the polygon scanner. Therefore, the soundproof glass needs to satisfy strict optical specifications. Moreover, in the case of an opposed scanning system, which typically includes two optical systems facing each other across the polygon scanner, two sheets of soundproof glass are required, which causes an increase in cost. Further, if the polygon scanner and surroundings thereof are enclosed by the soundproof glass, the transmission of the hot air to the scanning lens is suppressed, but the heat stays inside a space enclosing the polygon scanner, which limits the rotation rate and the continuous rotation time of the polygon scanner.
A substrate of the polygon scanner may be cooled from below by a fan, or a metal-based cover having high heat conductivity may be placed over the polygon scanner to release the heat. Either method, however, causes an increase in cost.
As a method of preventing the transmission of the hot air to the scanning lens without using the soundproof glass, an airflow guide member or the like may be employed to direct hot airflows generated from the polygon scanner away from the scanning lens. To prevent the transmission of the heat from the polygon mirror to the scanning lens through which a beam deflected and scanned by the polygon mirror is transmitted, a stepped guide member may be provided between the polygon mirror and the scanning lens to guide the hot airflows generated by the rotation of the polygon mirror toward a space above the scanning lens, without obstructing the beam.
However, it is necessary to dispose the stepped guide member so as not to obstruct the beam that is incident on the polygon mirror from the light source, scanned with the rotation of the polygon mirror, and reaching the scanning lens. That is, a portion of the stepped guide member on the path of the scanned beam needs to have an opening. Through the open portion of the stepped guide member allowing the transmission of the scanned beam, therefore, the hot air from the polygon mirror also reaches the scanning lens, causing a small but not significant increase in temperature.